1. Technical Field
The invention relates to laser radar and passive imaging systems.
2. Description of the Related Art
Currently, there are a number of techniques for imaging with laser detection and ranging systems (LADAR). LADAR systems have the ability to collect high angular and range resolution imagery of camouflaged targets hidden in deep clutter. LADAR systems use a laser to illuminate an area of interest and, therefore, the resulting imagery is not affected by variations in background illumination or self-emission. However, if detected, the laser emission may be used to locate the position of the LADAR system. Furthermore, because the LADAR is typically designed with a limited amount of available laser power, LADAR systems generally operate over a narrow field-of-view (FOV).
Passive imaging systems, however, operate using the available background illumination from light sources such as the sun or self-emissions of radiation from a target. Because these radiation sources are subject to unpredictable variations for most cases, images derived from passive imaging systems may not be reliable. These variations may also lead to high false-alarm rates. Passive imaging systems, however, are covert because they do not rely on emissions of energy from the detection system to form an image. Furthermore, passive imaging systems may be designed with focal planes that contain a large number of pixels. Therefore, passive imaging systems typically have a wider FOV than LADAR systems.
Examples of laser detection, ranging, or passive imagery are disclosed in U.S. Pat. Nos. 5,608,514 (Stann et. al.), 5,877,851 (Stann et. al.), 6,618,125 (Stann), 6,844,924 (Ruff et. al.), and 6,522,393 (Higashino). Further, for example, U.S. Pat. No. 5,608,514 discloses a system where a detector is followed by a signal mixer; 5,877,851 discloses a system where an electro-optic light modulator is positioned in front of a detector; and 6,844,924 discloses a self-mixing detector, which is also referred to as a metal-semiconductor-metal or an MSM detector. All of the above patents are fully incorporated herein by reference.